Movable coil electrical instrument



Feb. 26, 1952 K. J. KNUDSEN 2,586,831

MOVABLE COIL EI\..ECTRICAL INSTRUMENT Filed May 20, 1948 2 SHEETS--SHEET 1 INVENTOR. Knudsen ATTORNEYJ' Feb. 26, 1952 K. J. KNUDSEN MOVABLE COIL ELECTRICAL INSTRUMENT Filed May 20, 1948 2 SHEETSSHEET 2 Jay? I. W .11 N

. Hm' I v INVENTOR. Jfmza J,

lfrzudmem ATTORNEMS Patented Feb. 26, 1952 MOVABLE COIL ELECTRICAL INSTRUMENT Knud J. Knudsen, Naugatuck, Conn., assignor to The Lewis Engineering Company, Naugatuck, Conn., a corporation of Connecticut Application May 20, 1948, Serial No. 28,248

23 Claims.

This invention relates to electrical dnstruments of the movable coil type.

In my Patent #2,39l,i68 entitled Electrical Ratio Meter I disclose a meter providing uniform scale deflection over an are at least as great as 90 and having a movable coil assemblage comprising a deflecting and a restoring coil, which assemblage is completel installable and removable as a unit without dismantling or disturbing the magnet, pole or core structure of the instrument. Ratio meters having these characteristics are advantageous from the standpoint of the user because of the relatively large, uniform and therefore easily readable scale, and also from the standpoint of the manufacturer and the serviceman because of the removability of the movable coil assemblage without dismantling the magnet structure.

In the device disclosed in my patent above identified the movable coils iwere defiectable from an electrically centered position through an are at least as great as 45 in each direction, the limits of deflection being determined by obstruction of the opposite sides of the deflecting coil by a projection from the core of the instrument, by which the core was supported.

The deflecting coil, due to winding requirements was substantially rectangular in shape, and since it surrounded the core the blocking of movement of the coil by engagement with the core projection definitely limited the total deflection of the instrument; however, even if it were practically feasible to wind the coil so that it was not rectangular and substantially planar but instead bi-planar in shape or angular when viewed edgewise, the extent of deflection would still be limited to a value very considerably below 180,and such accomplishment of greater deflection would be had at the expense of simplicity and economy of construction, due in large part to the cost of producing coils of bi-planar shape.

An object of the present invention is to provide an improved, practical ratio meter having a coil assemblage installable and removable as a unit Without disturbing the magnet structure, and having a uniform scale deflection characteristic over an extended or very large arc, very substantially in excess of 90 and even as great as 300 or more.

Another object of the invention is to provide an improved commercially practical D. C. instrument or meter having a single movable coil form, which instrument has a uniform deflection characteristic over an extremely large are very substantially in excess of 90 and as great as 300 or more, characterized by removability of the coil assembly without disturbing the magnet assembly.

A still further object of the invention is to provide improved movable coil instruments as above characterized, which are simple and economical in construction and extremely reliable in operation at all times.

In accomplishing the above objects I provide, in accordance with the invention, novel instrument structures having coils and cooperable fluxproducing means, characterized by ring-like flux-carrying members which extend through. and link the coils and which have cuts through them, made large enough to pass the sides of the coils and arranged to enable the coils to be completely removed from the flux-producing means without dismantling or disturbance thereof.

I employ, in producing a ratio meter of extremely large, uniform scale deflection and coil assemblage which is removable without disturbing the flux-producing means or magnet structure, two separate flux-producing means in different sections of the instrument movement, one means being cooperable with the deflecting coil and the other with the restoring coil, the said coils being carried on a single shaft in fixed, axially spaced relationship. Each of the separate flux-producing means has a ring-like flux-carrying member adapted to extend through and link the associated coil, and having a cut through it arranged to provide for removability of the coils.

The deflecting-coil section of the instrument movement, in the specific embodiment of the invention illustrated herein, comprises a pair of permanent bar magnets, aligned with each other with a pair of like poles juxtaposed, and comprises a pole extension in the form of a ring having a projection interposed between the said juxtaposed poles. A second pole extension is provided, connected with the remote like poles of the bar magnets, the said second extension having an inner generally cylindrical pole face approximately concentric with and encircling the first pole extension and spaced therefrom. The deflecting coil is adapted to travel in an arcuate path along the surfaces of the'pole extensions, through an are which may be as great as 330, the pivotal axis of the coil being substantially coincidental with the axis of the ring-like pole extension which links the coil.

By this organization a field or flux of substantially uniform value may be established in the air gap between the pole extensionsthe gap being substantially of annular shape and the lines of flux extending mainly in radial directions and acting on the coil in a manner that the movement of force exerted by the coil is proportional to the energizing current thereof for most all deflected positions of the coil. The cut in the first ring-like pole extension (which links the coil) is preferably on a bias, that is, it extends angularly through the extension, and thus there is avoided a spot 3 the air gap adjacent the out which would be without flux to act on the coil.

The restoring coil section of the ratio meter instrument movement comprises a single permanent bar magnet having bifurcated poles corresponding portions of which lie opposite each other, and comprises a ring-like or C-shaped core member adapted to extend through and link the restoring coil. The core member extends between the divided portions of the bifurcated poles, and the restoring coil (which is secured to the same shaft as the deflecting coil and lies wholly to one side of said shaft) is movable in a path defined by the air gap between the poles and core. The restoring coil when energized is normally centered between the ends of the core, and the latter is shaped to provide a progressively increased flux for acting on the coil as it deflects in either direction from the centered position.

The spaces between the bifurcated poles of the single bar magnet and between the ends of the C-shaped core are large enough to pass a side of the restoring coil; also, the cut in the ringlike pole extension of the deflecting coil section is large enough to pass opposite sides of the restoring coil one after the other, and therefore the deflecting and restoring coils may be removed as a unit from their respective ring-like members in an axial direction, the restoring coil passing not only through the spaces between the core ends and bifurcated poles but also through the cut of the pole extension which normally links the deflecting coil.

In another illustrated embodiment of the invention, comprising a D. C. instrument of large uniform scale deflection with coil removability feature, a single deflecting coil section is provided, in many respects similar to the deflecting coil section of the ratio meter but having the cut in the coil-linking member extending through an extremely large arc whereby a very uniform flux value exists throughout the entire path of travel of the deflecting coil, without any areas of decreased flux. Thus a 300 deflection over a uniform scale is readily had yet the movable coil assembly may be installed or removedwithout disturbing the magnet assembly.

Other features and advantages will hereinafter appear.

In the accompanying drawings:

Figure l is an axial sectional view through an improved ratio meter made in accordance with the invention.

Fig. 2 is a front elevational view of the meter, showing the greatly extended uniform scale, and

indicating the large extent of movement of the movable coil assembly.

Fig. 3 is a transverse section taken on line 3-3 of Fig. 1.

Fig. 4 is a transverse section taken on line 4-4 of Fig. 1.

Fig. 5 is a fragmentary side elevational view showing the structure by which the separate fluxproducing means of the instrument movement are supported.

Fig. 6 is a fragmentary sectional view taken on line 66 of Fig. 3.

Fig. 7 is a front elevational view of one part of a pole extension of the deflecting coil section in the instrument movement.

Fig. 8 is an end view of the pole extension part shown in Fig. 7.

Fig. 9 is a transverse sectional view through a D. C. instrument having a single deflecting coil,

showing the coil and magnet assembly in front elevation.

Fig. 10 is a fragmentary bottom sectional view taken on line Ill-l0 of Fig. 9.

Fig. 11 is a side elevational view of part of a pole extension of the instrument of Fig. 9, and

Fig. 12 is a plan view of the part shown in Fig. 11.

Referring to Figs. 1 through 4 the improved ratio meter of the present invention comprises a cylindrical casing 20 having at its front end a transparent window 2| and at its rear end an insulating wall or closure plate 22 provided with a male connector fitting 23.

Intermediate the ends of the casing 20 a transverse supporting wall 24 of insulating material is provided, on the front of which is mounted the novel and improved instrument movement of the invention.

In accordance with the invention the improved instrument movement, which includes a deflecting and restoring coil, is so organized that an extremely large deflecting movement of the coils is had, substantially in excess of and as much as 300 or more, and the movement of the coils is so effected as to make possible the use of a uniformly graduated scale no portion of which is either substantially condensed or expanded, thus providing for easy reading of the instrument. In addition, the organization is such that the movable coils, which are fixedly secured to each other in a unitary assembly may be removed as a unit from the instrument movement without dismantling or disturbing the magnet assembly thereof, comprising the flux-producing means, pole extensions, core etc.

A very material advantage results from such an organization for several reasons. From the standpoint of a user, the uniformity of the scale enables readings to be very quickly and easily made, and the large extent of the scale, and of the deflecting movement of the coils enables a high degree of accuracy to be obtained in the readings. From the standpoint of the manufacturer such an improved organization results in a more rugged and reliable, higher quality instrument, and in a desirable economy in the manufacture of the instrument, since the magnet asesmblies may be completely fabricated as a unit, tested and properly adjusted prior to installation of the moving coil assembly. Then, in the later steps of fabrication of the instrument, coil assemblies may be installed, tested, removed and replaced etc. without alteration in the least of the flux producing and conducting means of the instrument movement. Also, in the event that servicing of the instrument movement is necessary at a later time, this is greatly facilitated by the coil-renlovability feature.

Referring to Fig. 1, the novel ratio meter instrument movement comprises two main sections, a restoring coil section 25 located immediately in front of the supporting wall 24, and a deflecing coil section 26 located in front of the restoring coil section 25.

As shown in Figs. 3, 4 and 5 the two sections 25 and 2B are supported by side brackets 27 having flanges 28 which are bolted to the intermediate supporting wall 24. In the deflecting coil section 26 the brackets 21 are bolted to a generally U-shaped member 29 of magnetic material, which constitutes a pole extension for the fluxproviding means of the deflecting coil section, as will be later brought out in detail. The member or pole extension 29 has bolted to it at its front the base of a bracket 3| formed of a generally triangular shaped stamping and bent somewhat in the shape of a U, the bracket 3| having a front portion or leg 32 on which is mounted a circular scale 33. At its extremity the leg 32 carries the usual pivot bearing assembly 34 for accommodating one of the pivots 35 of a shaft 36 comprising part of the movable coil assembly of the instrument.

The restoring coil section 25 of the instrument movement includes a supporting bar or block 31 which is bolted to the brackets 21, the bar being of non-magnetic material, preferably brass, and having bolted to it the base 38 of a bracket 39, which is generally similar to the bracket 3 being formed from a triangular shaped stamping and bent into substantially a U-shape. The bracket 39 has a rear portion or leg 40 the extremity of which carries a bearing assembly 4| for a pivot 42 mounted on the rear end of the shaft 36 of the moving coil assembly.

Referring to Figs. 1 and 4, the restoring coil section of the instrument further comprises a permanent bar magnet 43 located on the opposite side of the shaft 36 from the sup-porting bar 31, the magnet 43 being carried by a pair of pole extensions 44 which are preferably identical with each other and are shaped to provide bifurcated poles for the magnet. The pole extensions 44 may be formed from sheet metal, and each comprises an elongate flat strip-like base portion 45 the ends of which respectively engage corresponding ends of the supporting bar 31 and the bar magnet 43. Each base portion 45 has integral therewith and extending laterally thereof a pair of elongate fiat face portions 45 which are parallel to each other and in spaced relationship, the ends of the bar magnet 43 being interposed between corresponding ends of the face portions 45 and closely fitting thereto in intimate engagement. Slots 4'! are provided between the face portions 45 and the base portions 45 of the pole extensions, the said face portions being widened at their upper ends 48 as viewed in Fig. 4, and having a curved contour 49 between the wide and narrow parts.

The face portions 46 of the pole extensions 44 lie in parallel planes, and interposed between said face portions in spaced relationship thereto is a ring-like core member 50 having a wide cut in it to produce substantially a C or crescent shape, and having intermediate its ends a supporting projection 5| secured in the supporting bar 3'! whereby the core is rigidly mounted in its position. The ends 52 of the core 50 are spaced apart a substantial distance as shown, as are also the pole extensions 44 in the region of the core ends.

For reaction with the flux or magnetic field existing between the pole extensions 44 and the core 50 a generally rectangular-shaped restoring coil 53 is provided, rigidly mounted on the shaft 36, the coil being sized to fit between the face portions 46 of the .pole extensions and to fit around the core 59, and being deflectable from the intermediate or centered position shown in Figs. 1 and 4 in either direction through an are slightly less than 180 and at least 165.

As the restoring coil 53 is deflected more and more in either direction from the centered position shown, it will be subjected to a progressively increased number of flux lines or to a progressively greater amount of flux, due to the shape of the core 50 by which it tapers to points at its ends 52 and is widest at its middle. When the restoring coil 53 is energized with a direct current; the flux thereof, reacting with the flux of the' bifurcated pole extensions 44 and core 59 will tend to make the coil remain in its centered position shown and will cause the coil to resist deflecting movement in either direction, the opposition offered by the coil increasing as the deflection increases from the centered position due to the coil cutting more and more lines of force as it deflects further and further.

The deflecting coil section of the instrument movement, referring to Figs. 1 and 3, comprises a pair of bar magnets 54 which are aligned with each other and have a pair of south poles in juxtaposition. Secured to the bar magnets 54 is a ring-shaped extension or pole member 55 having a radial projection 56 interposed between the juxtaposed south poles of the magnets and secured thereto. The member 55 thus is magnetically polarized, being as shown, a south pole. A second pole extension is provided, comprising the generally U-shaped magnetic member 29 previously mentioned, the second pole extension extending around the ring-like extension 55 in spaced relation thereto, and having an internal generally cylindrical pole face 51 adjacent the ring-like pole 55. The extension or pole member 29 has portions 58 secured to the remote.

north poles of the bar magnets 54 whereby the member 29 is magnetically polarized north, or opposite to the polarization of the ring-like member 55. The extension 29 also has internal projecting portions 59 to make more complete the inner cylindrical pole face 51, and it will be seen that a radial magnetic field of uniform flux density may thereby be established between the pole members 55 and 29.

In accordance with the invention the pole member 55 is provided with a bias or diagonal cut 60, Fig. 6, located opposite the projection 56 of the pole, the out being sufliciently large to pass a side of a generally rectangular deflecting coil 6| fixedly mounted on the shaft 35. The coil 5| is adapted to link the pole 55 and to be movable from the centered position shown in either direc\ tion along the surface of the poles 55 and 29 through a relatively great arc of at least By this organization, due to the substantially uniform flux distribution in the air gap between the poles 55 and 29 (except at the cut 69, as will be explained shortly) the deflecting moment exerted by the deflecting coil 6| will be proportional to the current carried by the coil.

The movable coil system of the ratio-meter movement is seen to comprise the unitary assemblage including the restoring coil 53, the deflecting coil BI and the comm-on shaft 36 rigidly carrying the said coils in axially spaced edge-toedge, substantially coplanar relation, and by virtue of the character of the magnetic fields to which the coils are subjected the deflection of the movable coil assemblage may be made proportional to the ratio of the current in the defleeting coil to current in the restoring coil for all deflected positions of the coils, as will be more fully described later. Since normally the current in the restoring coil is substantially a constant, the deflection of the movable coil system will. be generally proportional to the current fiowingin the deflecting coil 6 to provide for uniformity of the scale.

The size of the cut 66 in the ring-like core 55 is sufficiently large to pass both the front and rear sides 53a. and 5312 respectively of the restoring coil 53 in addition to passing the rear side 6|a of 7 the deflecting coil 6i, and by this organization it is possible, in accordance with the invention, to remove the entire movable coil assembly from the instrument movement without disturbing the magnet assemblies of the movement.

For example, if the bracket 3| is first removed, this will carry with it the scale 33 and the bearing assembly 34, after which it will be possible to move the coil assembly forwardly, the rear side Bid of the deflecting coil entering the cut 6|] in the ring-like pole 55 and the front and rear sides 53a and 53b of the restoring coil passing forwardly through the spaces between the bifurcated poles 44 and the core ends 52. The front and rear sides of the restoring coil 53 may then enter and pass through the cut 60 in the pole 55, enabling the entire movable coil assembly to be removed as a unit without disturbing the poles 29, 55, nor the magnets 54, and without disturbing the magnet 43, poles 44 and core 50. Removal of the bearing bracket 3| of course does not disturb any of the poles nor the flux produced thereby.

Such removal as just disclosed must take place of course when the instrument is outside of the casing 20, or if the movement is inside of the casing, when the transparent window 2| is not in place. In either case, the usual electrical connec- 1 tions to the deflecting and restoring coils, as

effected in the conventional manner through spiral hair springs 62, 63 and 64 as shown, must first be severed.

The provision of the diagonal cut 66 in the pole 55 results in a lesser flux existing adjacent the cut, and the effect of such lessened flux is minimized, according to the invention, by extend- 9 ing the cut along a bias or diagonal line instead of straight across the pole. The term diagonal as hereinafter used is intended to designate a direction following the curved surface of the pole but other than axially thereof. However, this diminution of flux is compensated for by the fact that the flux in the spaces between the poles 44 and core ends 52 of the restoring coil section is also weakened or made less, thereby weakening the opposition to deflection provided by the restoring coil. As a consequence of much compensation, it is possible to strike a balance and effect a uniformity of the scale at the center portion thereof, corresponding to the centered positions of the coils as shown in the figures.

It will thus be seen that by the present invention I have provided a ratio meter having extremely desirable characteristics and advantages, namely an extremely large range of deflection, a uniformity of the scale, and a complete removability of the movable coil assembly without dismantling or disturbing the magnet assemblies of the instrument movement.

Referring to Fig. 2, showing the front of the scale 33, and showing the pointer 65 carried by the shaft 36, it will be seen that the scale graduations cover an arc of approximately 300, which is considerably greater than any heretofore provided in a ratio meter having the above advantages, and that the scale is uniformly graduated.

The pointer 65 is shown by full lines in the position corresponding to the centered positions of the deflecting and restoring coils, and is shown by dotted lines at one extreme deflected position wherein it is approximately beyond the end graduation of the scale. Therefore it will be noted that the movable coil system of the instrument movement of this invention has a maximum deflection in the neighborhood of 330.

For convenience and economy of manufacture,

the ring-like pole member may be formed of two pieces as shown, one of said pieces bein pictured in detail in Figs. '7 and 8 and comprising a semi-circular portion and a straight portion, the latter forming part of the projection 56 mentioned above. The semi-circular portion at its extremity has a sloping edge 66 forming one of the walls of the diagonal cut 60 defined as being in the pole member 55.

In accordance with the invention an advantageous D. C. instrument movement of the single coil type may be had by utilizing an organization very similar to the deflecting coil section 26 of the ratio meter described above, but with slight modifications. Such an instrument movement is shown in Figs. 9 through 12 and comprises. a deflecting coil 61 pivotally carried by a shaft 68, the coil linking a ring-like pole member 69 having a radial projection 10 secured between the juxtaposed like poles of a pair of aligned permanent bar magnets H. The ring-like pole 69 is encircled by a second pole 1'2 having portions 13 engaging the remote like poles of the bar ma nets "H.

According to the invention the ring-like pole 69 is provided with a helical or diagonal slot 14 which extends in a helix and is substantially coextensive with the air gap 15 between the poles 65 and 12. Preferably, for convenience of manufacture, the pole 69 is formed of two parts as shown, one of said parts being pictured in detail in Figs. 11 and 12 and having a circular portion 69a of tapered shape, and a radial projection 10a forming part of the projection 10 secured between the magnets H. The slot or cut M in the pole 69, constituting in effect the space between the circular portions of the two parts of the pole, is sufficiently wide to pass a side of the deflecting coil 61, thereby to enable the coil to be completely removed from the instrument movement without dismantling or disturbing the magnet structure comprising the magnets H and poles 69 and 12.

The air gap 15 between the poles will have a radial magnetic field in it of uniform value, the uniformity of the field being obtained by virtue of the fact that at any point in the path of travel of the coil 61 the combined outer exposed area of the pole 69 adjacent said point (facing the opposite pole) will be equal to a constant. By this organization an advantageous movable coil instrument is provided having an extremely large extent of deflection, having uniformity of the scale throughout, and providing for removability of the removable coil assembly without disturbing the magnet structure.

Variations and modifications may be made within the scope of this invention and portions of the improvements may be used without others.

I claim:

1. In a large deflection electrical instrument of the movable coil type, means including a pair of aligned bar magnets spaced from each other and having juxtaposed and remote pairs of like poles providing magnetic flux; a first, ring-like magnet pole having a projection extending between and secured to the juxtaposed like poles of said magnets; a second pole having spaced projections which extend outside of and are secured to the remote like poles of said magnets, said second pole being spaced from, and extending along said first pole; a movable coil through which the first pole extend and which it links; and means for mounting the movable coil for pivotal movement in a path along the surfaces of said poles, said coil and poles being arranged to enable the coil to travel over an arc of at least three right angles.

2. In an electrical instrument of the movable coil type, means providing magnetic flux; a first ring-like magnet pole secured to said means; a second pole secured to said means, spaced. from and extending along said first pole; a movable coil through which the first pole extends and which it links; and means for mounting the movable coil for pivotal movement in a path along the surfaces of said poles, said means being operable to release the coil for removal, andsaid first pole having a cut through it large enough to pass a side of the coil and enable the coil to be removed from the poles without disturbing the latter, said out extending in an angular direction between those opposite sides of the pole which are disposed generally edgewise to the second pole, and extending along a portion of the length of the ring-like pole whereby flux lines are provided for cutting the coil at all points around the pole regardless of the presence of' the cut.

3. In an electrical instrument of the movable coiltype, a deflecting coil; means for mounting the coil for pivotal movement in a path covering an are substantially greater than 129; and

means providing a magnetic flux acting on said coil throughout its path of movement to cause the coil to exert a moment having a constant ratio to the current in the coil for substantially all deflected positions thereof, said means including a magnet, a first ring-like magnet pole and a second magnet pole having a cylindrical inner surface spaced from and extending along the outside of said first pole, both said poles being secured to said magnet, said first pole linking the coil and having a cut through it large enough to pass a side of the coil and enable the coil to be removed from the poles without disturbing the latter, said out extending between op osite, axially-spaced sides of the pole and along substantially the entire length of the pole, and being of substantially uniform width throughout its length.

4. In an electrical instrument, a movable coil; m ans for mounting the coil for pivotal movement, said means being operable to release the coil for removal; and means providing a uniform magnetic flux acting on'said coil substantially throughout its movement, said means including a source of flux, a ring-like pole connected with said source, said pole linking and extending through said coil, and including a second pole connected with said source, spaced from and extending along said ring-like pole, the latter having a cut through it large enou h to ass a side of the coil and to enable the coil to be removed from said ilux-providingmeans without disturbing the latter, said out extending between the opposite sides of the pole which are disposed generally edgewise to the second pole, extending along substantially the entire length of the ringlike pole and having a substantially uniform width throughout its length.

5. In an electrical instrument, a movable coil; means for mounting the coil for pivotal movement in a predetermined circular path substantially greater than 120", said means being operable to release the coil for removal; and means providing a uniform magnetic flux acting on said coil substantiallythroughout its path of movethrough it, extending in anaro coextensive with the path of movement of the coil, and large, enough to pass one side of said coil and enable the coil to be removed from said flux-providing means without disturbing the latter, said out extending between the opposite sides of the pole which are disposed generally edgewise to the sec-- ond pole.

6. In a large deflection electrical instrument of the movable coil type, a pair of aligned permanent bar magnets having one pair of like poles in proximity to but spaced from each other; a ring-like pole extension having an outward projection interposed between and engaging said proximate like poles; a second pole extension extending outs side of and engaging the remotely located poles of the magnets, said second pol-e extension hav-- ing a circular surface extending along the ring,- like extension in spaced relation thereto; a movable coil linking said ring-like extension; andmeans for mounting the movable coil for pivotal movement in a path along the surfaces of said pole extensions, said means being operable to release the coil for removal, and said ring-like extension having a cut through it large enough to pass a side of the coil and enable the coil to be removed from the extensions without disturbing the latter, said coil and poles being arranged to enable the coil to travel over an arc of at least three right angles, and said out extending in an, angular direction between those opposite sides of the pole which are disposed generallyedgewise to the second pole, and extending along a portion of the length of the ring-like pole whereby flux lines are provided for cutting the coil at all points around the pole regardless of the presence of the out.

7. In an electrical instrument, a movable coil; means for mounting the coil for pivotal move-- ment in a predetermined circular path substantially greater than about an axis located outside of the coil and lying substantially in the plane thereof, said means being operable to release the coil for removal; and means providing a magnetic flux acting on said coil throughout its path of movement, said means including a source of flux, a ring-like pole connected with said source, said pole linking and extending through said coil and having an axis su stantially coincidental with the pivotal axis of the coil, and including a second pole connected with said source, spaced from and extending along said ring-like pole, the latter having a spiral cut through it, extending in an arc coextensive with the path of movement of the coil, and large enough to pass one side of said coil'and enable the coil to be removed from said flux-providing means without disturbing the latter, said out extending between those opposite sides of the pole which are disposed generally edgewise to the second pole whereby the flux pattern between the poles is controlled by the width of the cut.

8. In an electrical instrument of the movable coil type, a pair of aligned, permanent bar magnets having one pair of like poles in proximity to but spaced from each other; a ring-like pole extension comprising a pair of members having curved parts portions of which are spaced from and coextensive with each other, said members having juxtaposed projections interposed between and engaging said proximate like poles; a second pole extension engaging the remotely located pol-es of the magnets, said second pole extension having a circular surface extending along the 11 ring-like extension in spaced relation thereto and equispaced from the said portions of the members of said extension; a movable coil linking said ring-like extension; and means for mounting the movable coil for pivotal movementin a path along the surfaces of said pole extensions, said means being operable to release the coil for removal, and the space between the said coextensive portions of the members being large enough to pass one side of said coil and enable the coil to be removed from the extensions without disturbing the latter, said space controlling the flux pattern between the pole extensions.

9. In an electrical instrument of the movable coil type, first and second magnetic poles having opposite, concentric, generally cylindrical pole faces spaced from and coextensive with each other and extending through an are substantially greater than 120, said first pole having a ringlike shape; a magnet connected with said poles; a movable coil linkin said first pole; and means for mounting said coil for movement in a circular path substantially about the axis of the first pole and along the said pole faces, said means being operable to release the coil for removal and said ring-like pole having a spiral cut through it large enough to pass one side of the coil and enable the coil to be removed from the poles without disturbing the latter, said out extending between opposite, axially-spaced sides of the pole, and extending through an are substantially greater than 120 whereby the flux pattern between the poles throughout said are is controlled by the width of the cut. I

10. In a ratio meter, flux-providing means including a first, ring-shaped magnet pole and a second magnet pole spaced from and extending along said first pole; a deflecting coil linked by the first pole; a restoring coil rigid and substantially coplanar with the deflecting coil for simultaneous movement therewith; means for mounting said coils for movement about an axis, said coils being spacen apart longitudinally of the axis and the deflecting coil being movable along said poles; a magnet having spaced bifur- A cated poles corresponding portions of which lie opposite each other, the restoring coil being receivable between said portions; and a c-shaped core adapted to extend through and link the restoring coil and extending between said pole portions, the ends of the core and the bifurcated poles being, at adjacent points, respectively spaced apart enough to pass a side of the restoring coil, said first pole having a cut through it, substantially aligned with the spaces between the core ends and bifurcated poles and large enough to pass sides of both said coils one after the other, thereby to enable both said coils to be removed simultaneoosly as a unit without disturbing said poles, core, magnet or flux-providing means.

11. In a ratio meter, a moving coil assembly comprising pivotally mounted, relatively fixed deflecting and restoring coils spaced apart along a common pivotal axis and having a fixed angular relationship about said axis; means providing flux acting unidirectionally on the deflecting coil throughout its arc of movement, and separate means providing flux acting on the restoring coil,

in one direction throughout substantially onehalf its arc of movement, and in another direction throughout substantially the other half of said are of movement, both said flux-providing means including ring-shaped flux-carrying members extending around the coil axis and adapted to link the respective coils, said members havin a 12 cuts through them large enough to pass the sides of the coils and having generally the same angular relationship about said axis as said coils whereby the moving coil assembly is removable without disturbing said flux-providing means or the flux carrying members thereof.

12. In a ratio meter having uniform scale deflection, a moving coil assembly comprising a shaft and deflecting and restoring coils fixed to, and spaced apart longitudinally of, the shaft, said coils having a fixed angular relationship about the shaft and being simultaneously movable through arcs substantially greater than means providing mainly a uniform density of flux acting unidirectionally on the deflecting coil throughout its arc of movement; and separate means providing a progressively increasing density of flux acting on the restoring coil in one direction throughout substantially one-half its arc of movement from an intermediate position, and acting in another direction throughout substantially the other half of said are of movement from said position, said flux-providing means ineluding respectively a ring-shaped pole member and a ring-shaped core member extending around the shaft and adapted to link the respective coils, said members having cuts through them large enough to pass the sides of the coils and having generally the same angular relationship about said shaft as said coils whereby the moving coil assembly is removable without disturbing said flux-providing means or the pole or core member thereof.

13. In a ratio meter, flux-providing means including a first, ring-shaped magnet pole and a second magnet pole spaced from and extending along said first pole; a deflecting coil linked by the first pole; a restoring coil rigid and substantially coplanar with the deflectin coil for simultaneous movement therewith; means for mount-v ing said coils for movement about an axis, said coils being spaced apart longitudinally of the axis and the deflecting coil being movable along said poles; and separate flux-providing means acting on the restoring coil in one direction throughout substantially one-half its arc of movement, and in another direction throughout substantially the other half of said are of movement, said separate means including a ring-shaped flux-carrying member adapted to link the restoring coil and having a cut through it, large enough to pass a side of the coil, said first magnet pole having a cut through it, substantially aligned with the cut in said ring-shaped member and large enough to pass a side of the deflecting coil, and one of said cuts being large enough to pass sides of both said coils one after the other, thereby to enable said coils to be removed simultaneously as a unit without disturbing said poles orrflux-providing means. 7

14. In a ratio meter, a moving coil assembly comprising edgewise disposed, pivotally mounted, relatively fixed deflecting and restoring coils spaced apart along their pivotal axis, means providing flux acting unidirectionally on the deflecting coil throughout its arc of movement; a magnet having spaced bifurcated poles corresponding portions of which lie opposite each other, the restoring coil being receivable between said portions; and a C-shaped core adapted to extend through and link the restoring coil and extending between said pole portions, the ends of the core and the bifurcated poles being, at adjacent points, respectively spaced apart enough to pass a side of the restoring coil, said flux-providing asaaasr means including a ring-shaped member adapted to link the restoring coil and having a cut through it, large enough to pass a side of the coil, either said'cut or the said spaces between the coreends and bifurcated poles being large enough to pass sides of both said coils one after the other, thereby to enable said coils to be removed simultaneously as a unit without disturbing said poles, core, magnet or flux-providing means.

15. In a ratio meter having uniform scale de fiection, a moving coil assembly comprising edgewise disposed, pivotally mounted, relatively fixed deflecting and restoring coils spaced apart along a common pivotal axis and having a fixed angular relationship about said axis, said coils being simultaneously movable through are substantially greater than 120; means providing mainly a uniform density of flux acting unidirectionally on the deflecting coil throughout its arc of movement; and separate means providing progressively increasing density of flux acting on the restoring coil in one direction throughout substantially one-half its arc of movement from an intermediate position, and acting in another direction throughout substantially the other half of said are of movement from said position, both said flux-providing means including ring-shaped fluxcarrying members extending around the coil axis and adapted to link the respective coils, said members having cuts through them large enough to pass the sides of the coils and having generally the same angular relationship about said axis as said coils whereby the moving coil asembly is removable without disturbing said flux-providing means or the flux-carrying members thereof. I

16. In a ratio meter having uniform scale deflection,- a moving coil assembly comprising pivotally mounted relatively fixed deflecting and restoring coils spaced apart along a common pivotal axis and having a fixed angular relationship about said axis, said coils bein simultaneously movable through an arcsubstantially greater than 120; and means providing magnetic fluxes acting on said coils throughout their paths of movement to. cause the deflection of the coils to be substantially proportional to the ratio of current in the deflecting coil to current in the restoring coil for any deflected position thereof, the flux acting on the deflecting coil being mainly of uniform density and acting unidirectionally thereof and the flux on the restoring coil acting in one direction and being of progressively increasing densitythrough substantially one-half the arc of movement of the coil from an intermediate position, and acting in another direction and being of progressively increasing density through substantially the other half of said are of movement from said position, said flux-providing means including ring-shaped flux-carrying members extending around the coil axis and adapted to link the respective coils, said members having cuts through them large enough to pass the sides of the coils and having generally the same angular re1ationship about said axis as said coils whereby the moving coil assembly is removable without disturbing said flux-providing means or the fluxcarrying members thereof.

17. In a ratio meter, flux-providing means including a first, ring-shaped magnet pole and a second magnet pole spaced from and extending. along said first pole; a deflecting coil linked by the first pole; a restoring coil rigid and substantially coplanar with the deflecting coil for simultaneous movement therewith; means for 14 mounting said coils for movement about an axis, said coils being spaced apart longitudinally of the axis and the deflecting coil being movable along said poles; a magnet having spaced bifurcated poles corresponding portions of which lie opposite each other, the restoring coil being receivable between said portions; and a C-shaped core adapted to extend through the restoring coil and extending between said pole portions, the ends of the core and the bifurcated poles being, at adjacent points, respectively spaced apart enough to pass a side of the restoring coil, said first pole having a diagonal cut through it, located alongside the spaces between the core ends and bifurcated poles, said spaces being sub stantially wider than the sides of the restoring coil and said diagonal out being large enough to pass sides of both said coils one after the other, thereby to provide clearance for the coils to be tilted and removed as a unit through said diagonal out without disturbing said poles, core,

magnet or flux-providing means.

18. In a ratio meter, flux-providing means including a first, ring-shaped magnet pole and a second magnet pole spaced from and extending along said first pole; a deflecting coil linked by the first pole; a restoring coil substantially coplanar with the deflecting coil; means including a shaft, rigidly connecting the coils together for simultaneous movement about an axis, said,

coils having substantially rectangular contours the lengths of which are at right angles, said coils being spaced apart longitudinally of the said axis, and being located on the same side of the shaft, and the deflecting coil being movable along said poles; a magnet having spaced bifurcated poles corresponding portions of which lie opposite each other, the restoring coil being receivable between said portions; and a C-shaped core adapted to extend through the restoring coil and extending between said pole portions, the ends of the core and the bifurcated poles being, at adjacent points, respectively spaced apart enough to pass a side of the restoring coil, said first pole having a cut through it, located opposite the spaces between the core ends and bifurcated poles and large enough to pass sides of both said coils one after the other, thereby to enable both said coils to be removed simultaneously as a unit without disturbing said poles. core, magnet or flux-providing means.

19. In a ratio meter, flux-providing means including a first permanent magnet, a first, ringshaped magnet pole and a second magnet pole spaced from and extendin along said first pole; a deflecting coil linked by the first pole; a restoring coil rigid and substantially coplanar with the deflecting coil for simultaneous movement therewith; means for mounting said coils for movement about an axis substantially coinciding with the oi the ring-shaped magnet pole, said coils being spaced apart longitudinally 01" the axis and the deflecting coil being movable along said poles; a second permanent magnet having spaced bifurcated poles corresponding portions of which lie opposite each other, the restoring coil being receivable between said portions; and a c-shaped core adapted to extend through the restoring coil and extending between said pole portions, the core and pole portions being spaced axially from said first and second poles and the second permanent magnet being on a side of said axis opposite-to the first permanent magnet, the ends of the core and the assassr 15 bifurcated poles being, at adjacent points, respectively spaced apart enough to pass a side of the restoring coil, said first pole having a cut through it, substantially aligned with the spaces between the core ends and bifurcated poles and large enough to pass sides of both said coils one after the other, thereby to enable both said coils to be removed simultaneously as a unit without disturbing said poles, core, magnet r flux-providing means.

20. In a ratio meter, flux providing means including a first, ring-shaped magnet pole and a second magnet pole spaced from and extending along said first pole; a deflecting coil linked by the first pole; a restoring coil rigid and substantially coplanar with the deflecting coil for simultaneous movement therewith; means for mounting said coils for movement about an axis, said coils being spaced apart longitudinally of the axis and the deflecting coil being movable along said poles; a magnet having spaced bifurcated poles corresponding portions of which lie opposite each other, the restoring coil being receivable between said portions; and a c-shaped core adapted to extend through the restoring coil and extending between said pole portions, the ends of the core and the bifurcated poles being, at adjacent points, respectively spaced apart enough to pass sides of both said coils one after the other, said first pole having a cut through it, substantially aligned with the spaces between the core ends and bifurcated poles and large enough to pass a side of the deflecting coil, thereby to enable both said coils to be removed simultaneously as a unit without disturbing said poles, core, magnet or flux-providing means.

21. In a ratio meter, a moving coil assembly comprising edgewise disposed, pivotally mounted, relatively fixed deflecting and restoring coils spaced apart along a common pivotal axis, and lying in a common plane on the same side of said axis, said coils being simultaneously movable through arcs substantially greater than 120; means including a pair of aligned permanent bar magnets, providing flux acting unidirectionally on the deflecting coil throughout its arc of movement; and separate means including a single permanent bar magnet located on the opposite side of the pivotal coil axis with relation to the pair of bar magnets, providing flux acting on the restoring coil in one direction throughout substantially one-half its arc of movement, and in another direction throughout substantially the other half of said arc of movement, both said flux-providing means including ring-shaped flux-carrying members extending around the coil axis and adapted to link the respective coils, said members having substantially aligned cuts through them large enough to pass the sides of the coils whereby the 'moving coil assembly is removable without disturbing said flux-providing means or the flux-carrying members thereof.

22. In a ratio meter, a moving coil assembly comprising edgewise disposed, pivotally mounted, relatively fixed deflecting and restoring coils spaced apart along a common pivotal axis and lying in a common plane on the same side of said axis, said coils being simultaneously movable through arcs substantially greater than 120; means including a pair of aligned permanent bar magnets, providing flux acting unidirectionally on the deflecting coil throughout its arc of movement; and separate means including a permanent bar magnet located on the opposite side of the pivotal coil axis from the pair of bar magnets and including a pair of spaced bifurcated poles connected to the bar magnet, providing flux acting on the restoring coil in one direction throughout substantially one-half its arc of movement, and in another direction throughout substantially the other half of said are of movement, both said flux-providing means including ring-shaped flux-carrying members extending around the coil axis and adapted to link the respective coils, said members having substantially aligned cuts through them which, together with the spaces between said bifurcated poles, are large enough to pass the sides of the coils whereby the moving coil assembly is removable Without disturbing said flux-providing means or the fluxcarrying members and bifurcated poles thereof.

23. In a ratio meter having a uniform scale, flux-providing means including a first, ringshaped magnet pole having a cut through it and a second magnet pole spaced from and extending along said first pole, said means providing a flux of substantially uniform density in the air gap except at the out in said first pole; a deflecting coil linked by the first pole; a restoring coil rigid and substantially coplanar with the deflecting coil for simultaneous movement therewith; means for mounting said coils for movement about an axis, said coils being spaced apart longitudinally of the axis and the deflecting coil being movable along said poles; a magnet having spaced bifurcated poles corresponding portions of which lie opposite each other, the restoring coil being receivable between said portions; and a C-shaped core adapted to extend through and link the restoring coil, and extending between said pole portions, said core and poles providing a progressively increased density of flux when plotted against coil deflection, adapted to act on the restoring coil in one direction throughout substantially one-half its arc of movement from an intermediate position, and to act on the coil in another direction throughout substantially the other half of said are of movement from said position, the ends of the core and the bifurcated poles being, at adjacent points, respectively spaced apart enough to pass a side of the restoring coil and the cut in the first pole being substantially aligned with the spaces between the core ends and bifurcated poles and being large enough to pass a side of the deflecting coil to enable both said coils to be removed simultaneously as a unit without disturbing said poles, core, magnet 0r flux-providing means, and the flux density and flux distribution adjacent the cut in the first pole being related to the fiux density and flux distribution adjacent the spaces between the ends of the core and bifurcated poles to provide for uniformity in the graduations of the scale throughout the range of the latter. KNUD J. KNUDSEN.-

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 537,501 Ihomson Apr. 16, 1895 591,241 Shollenberger Oct. 5, 1897 967,597 Zander Aug. 16, 1910 1,171,907 Trent Feb. 15, 1916 2,438,027 Young et a1 Mar. 16, 1928 

